Immunologic characteristics of keratins in extramammary Paget's disease

Six cases of extramammary Paget's disease were immunohistochemically investigated with several antikeratin monoclonal antibodies. Paget cells and surrounding epidermal keratinocytes were equally stained with an antikeratin monoclonal antibody, HKN-4, which recognizes a broad spectrum of keratins. However, Paget cells were clearly distinguished from the surrounding epidermal keratinocytes by HKN-2, which does not react with keratins of secretory cells but does react with keratins of ductal and myoepithelial cells of sweat glands and with epidermis and hair tissue of the normal skin. The HKN-2 did not bind to Paget cells, but the surrounding keratinocytes were positive. CK7, LE41, RGE53, and LP2K, which recognize simple epithelium-type keratins 7 (molecular weight [MW], 54,000; type II), 8 (MW, 52,500; type II), 18 (MW, 45,000; type I), and 19 (MW, 40,000; type I), respectively, stained Paget cells but not the surrounding keratinocytes. Two cases of Merkel cell carcinoma, examined as controls, showed positivity to LE41 and RGE53 but not to CK7 and LP2K. Since in the normal skin the secretory cells of sweat glands showed the same keratin expression as that of Paget cells, Paget cells of extramammary Paget's disease may be derived from or differentiate to the secretory cells of sweat glands.